Field of the Invention
The present invention relates to an image capturing apparatus and a method for controlling the image capturing apparatus.
Description of the Related Art
In recent years, in the field of image capturing apparatuses employing a CMOS-type image sensor or the like, image capturing apparatuses have been proposed that can acquire not only an intensity distribution of light, but also an incident direction and distance information of light.
Japanese Patent No. 3774597 discloses technology whereby it is possible to perform focus point detection by a pupil division system. According to Japanese Patent No. 3774597, by dividing a photodiode (referred to below as a PD) of a unit pixel that corresponds to a single microlens into two photodiodes, it is possible for each PD to receive light of a different pupil plane of an image lens. Also, focus point detection is performed by comparing the output of two PDs. Also, by summing output signals from the two photodiodes that constitute the unit pixel, it is possible to obtain a normal shooting image.
Incidentally, in a case where each pixel has a plurality of PDs as in Japanese Patent No. 3774597, there is the problem that an increased amount of time is needed to read out signals from all PDs, so the frame rate decreases.
As a method for shortening the read out time of one frame, there is a method in which the pixels used for focus point detection are limited. For example, signals of divided PDs within a unit pixel are respectively read out only for a row used for focus point detection processing, and for a row not used for focus point detection processing, signals of divided PDs are summed and only a signal for image generation is read out, thus enabling an increase in read out time to be suppressed.
However, in this case, because the read out time differs between a row used for focus point detection processing and a row not used for focus point detection processing, in an ordinary slit rolling operation used as an operation when performing live view or moving image shooting, a phenomenon occurs that accumulation time, i.e. the amount of light exposure, differs by pixel row. Also, in the case of the driving method disclosed in Japanese Patent No. 3774597, because signals of divided PDs are read out at different times, there is also the problem that strictly speaking the timing of accumulation differs.